Relay circuit



A. H. LAMB RELAY CIRCUIT April 11, 1944.

Filed Jan. 50, 1942 2 Sheets-She et l April 11, 1944.

A. H. LAMB 2,346,589

RELAY CIRCUIT Filed Jan. 30, 1942 2 Sheets-Sheet 2 Patented Apr. 11, 1944 RELAY CIRCUIT Anthony H.

Newark, N. 1.,

Lamb, Elizabeth, N. J., assignor to Weston Electrical Instrument Corporation,

a corporation of New Jersey Application January 30, 1942, Serial No. 428,956 19 Claims. (Cl. 175-320),

This invention relates to relay circuit that include magnetic contact relays, and more particularly to relay circuits employing highly sensitive magnetic contact relays that are reset without the use of mechanical resetting mechanisms.

Magnetic contact relays such as disclosed in my prior Patents 2,014,385 and 2,014,386 have been used to control heavy load circuits in response to predetermined changes in a measured quantity or factor (such as temperature, illumination, voltage or current) that is too small to develop a reliable closure of non-magnetic contacts or to separate the magnetic contacts. As described in m prior patents, the moving system of the relay displaces the movable pointer and contact freely in the usual manner until the measured factor reaches the critical value at which the magnetic attraction between the contacts displaces the moving system, and the contacts then engage under magnetic attraction to afford a reliable non chattering contact closure. Some form of mechanical resetting mechanism has been required to separate the magnetic contacts when the subsequent changes in the measured factor were incapable of developing a force suflicient to separate the magnetic contacts, and these mechanical resetting mechanisms have imposed some limitations upon the design of the sensitive relays and upon the fields of use of the same.

An object of this invention is to providee relay circuit that includes one or more sensitive relays ofthe magnetic contact type, and circuit elements for resetting the relays without resorting to mechanical resetting mechanisms. An object is to provide a relay circuit including a sensitive instrument relay of the magnetic contact type with a moving system that responds to variations in a relatively minute control current, the magnetic attraction between the engaged contacts being substantially greater than any resetting force developed by the control current fluctuations, and a resetting circuit including a current source for momentarily establishing in the moving system a heavy current flow to overcome the magnetic attraction between the contacts. An object is to provide a sensitive relay circuit including an instrument relay with magnetic contacts, a current source for imposing upon the relay movin system a relatively minute current flow that varies with a control factor or quantity, and a resetting circuit for automatically sending a heavy current flow through the relay moving system upon an engagement of the magnetic contacts, whereby the load circuit of the so long as the control factor magnitude remains within a range corresponding to energization of the relay. An object is to provide a self-resetting relay circuit that includes a sensitive relay with magnetic contacts, a control current source connected across the moving system of the relay but developing forces insuflicient to reset the relay, and a resetting current source for supplying a heavy, short-duration current pulse to the relay moving system to reset the same upon an engagement of the magnetic contacts. More specifically, an object is to provide a relay circuit including a pair of magnetic contact relays, a load or load circuit controlled by the rela contacts, and a resetting circuit also controlled by said contacts to establish a current surge of relatlvely high value through the relays to reset the same. An object is to provide a self-resetting relay circuit including a pair of magnetic contact relays that operate in opposite sense in response to changes in the value of the control factor, a load controlled by the magnetic contacts of the relays, and a resetting circuit including a power source and circuit connections such that the closure of either set of magnetic contacts establishes a momentary current pulse of high magnitude through the relays to reset the same. More particularly, an object is to provide a selfresetting relay circuit including a Wheatstone bridge network having magnetic contact type relays in two side arms, a fluctuating source of control current in a conjugate arm of the network, a load circuit including a power current source and a load in series with the magnetic contacts of one relay, and a resetting circuit connected across the bridge as the other conjugate arm, the resetting circuit including the magnetic contacts of the second relay and a voltage drop resistor in the load circuit.

These and other objects and advantages will be apparent from the following description when taken with the accompanying drawings in which:

Figs. 1 and 2 are schematic circuit diagrams illustrating different embodiments of the invention;

Fig. 3 is a schematic diagram of a relay circuit in which the relay contact arm carries a magnetic contact cooperating with a pair of angularly spaced magnetic contacts, load devices selectively energized in accordance with the magnetic contacts that are closed, and a relay resetting circuit energized by a closure Of the relay contacts Fig. 4 is a diagram of a relay circuit in which relay is intermittently energized and de-energized the power current source for resetting the relay is electrically isolated from the control current source that is connected to the moving system of the relay;

Fig. 5 is a diagram of a modification of the relay circuit of Fig. 4;

Fig. 6 is a schematic diagram of a relay circuit of the on-ofl control type that includes two selfresetting sensitive relays of the magnetic contact type; and

Fig. '7 is a schematic diagram of an alternative arrangement that includes current sources individual to the load circuit and to the resetting 'amperes. For purposes of illustration, the current source 2 is shown diagrammatically as a thermocouple but it is to be understood that the control current source may be a photoelectric cell, a potentiometer, or the potential drop across a temperature-variant resistance, according to the character of the factor or quantity that is to control the relay circuit. The pointer 3 is secured to the coil i and carries a small rider or contact ii of magnetic material for cooperation with a relatively stationary magnetic contact The magnetized contact 5 is so positioned that the contact l is drawn into engagement with the contact 5 when the pointer 3 is moved to a preselected graduation or the scale ii by the flow of control current through the coil 8. A load-circuit including a current source l and a load device 8 is connected between the relay contacts d, 5.

The elements so far described are, or may be, of any desired type and relative arrangement. The load device 8 may be a visual or an audible signal, a motor, or a power relay according to the desired control or relay action. According to this invention, a heavy current is automatically supplied to the relay moving system at each contact closure to develop a torque greater than that required to overcome the magnetic attraction oi the engaged contacts.

The resetting current may be drawn from the power current source 7 of the load circuit by shunting the relay coil l across the load device 8, a resistor 9 being included in the coil branch of this parallel circuit network. to limit the resetting current fiow to a magnitude that will not damage the coil i. In general, the resetting current flow may be of the order of milliamperes when the reiy is designed for a control current input of the order of several microamperes. The control current source 2 is in shunt with the coil i, so far as concerns current flow from the power source l, and. a current limiting resistor id is placed in series with the source 2 to restrict the flow of power current through the source 2.

An engagement of ti magnetic relay contacts l, 5 closes the load circuit to energize the load device from the battery it, and also completes the resetting circuit through the resistor 9 and coil i. The polarity and magnitude or the resetting current flow through the relay coil i are such that the coil rotates clockwise to separate the magnetic contacts, thereby automatically separating the relay contacts 8, 5 to open the load circuit and the resetting circuit. The flow of resetting current is thus limited to a relatively short current pulse, and the resetting current may therefore be of a value substantially higher than the maximum current that could be passed through the coil l for an appreciable period without damage to the winding.

The Fig. l relay circuit is of the pulsing or periodic closing type as the energization of the load device 8 and the resetting of the relay moving system take place alternately so long as the current output of the control source 2 is within the range corresponding to a clesure of the relay contacts.

The flow of power current through the control source during the resetting operation may be objectionable in some cases, for example when the control current source 2' is a photoelectric cell.

The control current source may be efiectively isolated from the resetting current source by providing the moving system of the sensitive relay with a control winding i and a separate resetting winding ii, as shown schematically in Fig. 2. The remaining elements of the Fig. 2 circuit are, or may be, substantially identical with the corresponding elements of the Fig. 1 relay circuit.

The resetting system may be incorporated in a double contact or high-low relay circuit, such as shown in Fig. 3, in which the load devices 8, 8' are selectively energized by power cur rent sources l, 8 respectively in accordance with the engagement of the movable contact 3 with the magnet contact 5 or 5. The load devices 3, it are connected between the outer terminals of the power sources i, 'l' and the respective magnet contacts 5, 5', and the midpoint of the serially connected power sources is connected to the movable contact arm through a lead i2 and series resistor 83. The resistor i3 is shunted across the control current circuit that connects the variable current source 2 to the relay moving coil i, and current limiting resistors 9, it are arranged in the control circuit between the shunt resistor l3 and, respectively, the coil i and the current source 2.

The relatively heavy current that may he required for operation of the load devices 8, d flows through the resistor it; to establish a potential drop that is impressed across the moving coil E for resetting. The direction of load current flow through the resistor it depends upon the contact 5 or 5 that is engaged by the movable contact d, and the polarity of the resetting potential drop across resistor it therefore reverses in accordance with the required direction of rotation of coil i for a resetting operation. The reversed polarity of current iiow from the power current sources l, l to the load devices at, ii is not material as the current source and return circuit connections may be made to the proper terminals of each load device when a particular direction of current fiow through the device is required.

The double contact control circuit is of the pulsing type and is similar to the Fig. 1 circuit in that the moving system of the relay has a single coil 9 that is traversed by both the control current and the resetting current. The sep. a control and resetting windings oi the Fig. 2 circuit may be employed in the double contact relay sy- .em when an electrical isolation of the control and resetting circuits is desirable.

A bridge circuit arrangement, as shown in Fig. 4, may be em, oyed to obtain an electrical isolacontacts.

tion of the control and resetting currents without resorting to a double winding on the moving system of the relay. The relay winding l and resistors l4, l5, it are arranged as the side arms oi a bridge network, and one or more of the resistors are preferably adjustable for a balancing of the bridge network. A fluctuating control current source, for example a photocell 2, is connected across one set of opposed terminals of the bridge, and the load circuit includes the magnetic contacts l, 5, a current source 2, a power relay do, and a voltage drop resistor it that is connected across the other set of opposed bridge terminals by leads l8, id.

The control current from the photocell 2 and the resetting current from the power source l both how through the relay coil l but the control and resetting circuits are efiectively isolated when the bridge network balanced. The polarity of the potential drop across the resistor ii is of course such that the coil i is turned clockwise by the resetting current pulse. The polarity symbols adjacent the terminals of the photocell 2 and the resistor ll indicate that the relay contacts engage when the photocell current falls to a selected low value, and that the resetting current pulse is in the same sense as the low value photocell current. If the relay contacts close upon an increase of the photocell current to a critical value, the leads it must be reversed to pass the resetting current pulse through the coil 4 in opposition to the photocell current.

The self-resetting relay circuit of Fig. 5 is similar to the described Fig. l circuit, and corresponding parts are identified by like numerals but are'not described in detail. These alternative circuit arrangements are distinguished from each other by the particular circuit connections for introducing the resetting current pulse into the bridge network. In the Fig. 5 relay circuit, the opposed terminals of the bridge network are connected across the load circuit relay to through the current limiting resistor and the lead it. The resistor it will be of a relatively high value when the power current source i has a high voltage to establish a heavy current flow through the auxiliary relay to. The magnitude of the resetting current pulse is thus reduced to a safe value by the resistor l9 that is a series element of the resetting circuit. In Fig. 4, the voltage drop resistor I? will have a relatively low ohmic resistance to reduce the potential across the bridge network to a safe value.

The relays of the described circuits will pulsate continuously so long as the control current has a value corresponding to a closure of the relay The invention may be applied to onofi relay circuits by employing separate magnetic contact relays for the high and low contact closures. A typical relay circuit of this type, as illustrated in Fig. 6, may be generally similar to the described photoelectric relay circuit of Fig. 4 but differs therefrom in that the pivoted coil l of a sensitive instrument relay replaces the resistor I4 (Fig, 4) as one balancing arm of the bridge network. For convenience of description, the relay 20 which includes the moving coil I will be identified as the initiating relay, and the relay 20' will be identified as the resetting relay. The relays may be of identical design, although this is not essential, and the resetting relay includes a pointer 3 that carries a magnetic material contact 4' for cooperation with a magnetized contact 5, the pointer moving along system for controlling lights by the ing the power relay 8a which may resistor to one junction of a graduated scale 6' to indicate the instantane one value of the measured factor or current flow established through the coil i by the control current source or photocell 2.

The relays 2B, 20' are so designed or connected into the network that an increased current out put from the photocell 72' ll of the initiating relay 5, and moves the contact relay 28 towards the associated fixed contact 5'. The direction of current flow from the control current source 2' is indicated by the solid line arrows at, and inspection of the circuit dia gram shows that the magnetic contacts of the initiating relay close when the illumination at the photocell 2: drops to a selected critical value, and that the contacts ii of the resetting relay 23 close when the photocell iilu-= minatlon rises to a preselected critical value.

The controlled or load circuit between the relay contacts 4 and 5 includes, in series, the power current source l, the auxiliary relay to, and voltage drop resistor The lead 22 extends from the positive terminal of the voltage drop the bridge network, and lead 28 extends from the other terminal of resistor M to the contact arm 3 of the resetting relay 28, the contact 5' of relay being con nected to the opposite bridge terminal by a lead Inspection of the circuit diagram shows that a voltage drop will be established across resistor 26 by the current source 7 when the contacts 3 ii of relay 2c are closed, and that this voltage drop will establish a current flow iii-the bridge network when the contacts l, 5' of relay 2% are closed. The direction of this current now is indicated by the dotted line arrows b. The method of operation of the relay circuit will. be explained with respect to a photoelectric relay relay to in the photoaway from the contact arm 3 of the resetting accordance with the illumination at cell 2'.

For clarity, it will be assumed that the contacts of both relays are initially open. Such a balanced condition is obtained when the quantity of light falling upon the photocell 2' causes said cell to generate sufiicient energy to deflect the movable coils l, l of the sensitive relays so that the movable arms 3, 3 each occupy a position between graduated values 1 and 5 on the illustrated scales 6, G. This deflection may be predetermined for a given quantity of light'by proper choice of the bridge resistors l5, ill with respect to the resistance of the movable coils and the sensitivity of the relays. With the contacts of the initiating relays open, the power relay 8a is de-energized and no potential is impressed across the bridge network other than that generated by the photocell 2.

The current output of the photocell decreases with approaching darkness and the movable coils of both relays rotate in a counterclockwise direction as explained hereinabove. A sufficient decrease in cell output causes contacts 4, 5 or" the initiating relay 20 to close, thereby energizbe provided with suitable contacts to turn on artificial illumination as is well known in the art. Further decrease in the current output of the photocell is ineffective, tending only to move the movable arm 3' of the resetting relay toward the zero point on the scale. Inasmuch as the battery cir cult is completed by the closure of contacts 4,

moves the contact arm of relay 2%, a definite voltage drop exists across the resistor it.

With the approach of daylight the photocell generates an increasing current that tends torotate the movable coils of the sensitive relays in a clockwise direction. Contacts 3, 5 of the initiating relay remain closed as the photocell current does not produce sumcient-torque in the movable coil l to overcome the magnetic attraction between the contacts. However, movable coil 6' of resetting relay is free to move and the contacts 6' 5' therefore engage when the photocell current reaches the value for which the relay is calibrated. The closure of contacts 4', 5' impresses the potential which exists across the drop resistor 2i across the bridge network producing a flow of current as indicated by the broken line arrows b. This current is employed to reset the relay contacts and its magnitude depends upon the constants of the electrical circult, being in the order of milliamperes as compared to the microampere output of the photocell. Such a relatively large current develops sufilcient torque in the movable coils to cause separation of the relay contacts. Upon the opening of the contacts of the initiating relay 2d, the power relay 8a is de-energized and the potential drop across the resistor 2i is removed. The movable contact arm 3 of the initiating relay 2 6 now assumes an upscale position indicative of the current generated by the photocell. 0n the other hand, the movable arm 3 of the resetting relay Ell immediately re-engages with the magnet contact 5' without further efiect upon the circuit.

As darkness again approaches, the current output of the photocell 2' decreases, thereby tending to produce counterclockwise rotation of the movable coils i, i. The contacts l, 5' of the resetting relay 20' remain closed as current flow through the movable coil i is not sufiicient to overcome the magnetic attraction between the contacts 4i, 5'. The coil 6 of the initiating relay 20 is now free to rotate however; and the contacts l, 5 close when the output of the photo= cell decreases to the value for which the relay is calibrated. Closure of these contacts complates the power circuit, thus energizing the power relay 3a and establishing a voltage drop across the resistor 2!. As the contacts of the resetting relay have remained closed during this part of the operating cycle, the voltage now appearing across drop resistor 2! is immediately impressed across the bridge network and both relays consequently are reset, as explained hereinabove. Movable arm 3' of the resetting relay therefore assumes a low scale position indicative of the reduced photocell current iiowingthrough coil l and the contacts of the initiating relay 2d reclose immediately to keep the power relay 8a energized but the bridge network is unafiected because of the open contacts i, 5 of the resetting relay 28". a

It will be apparent that by proper choice of the values of the resistors i5, i6 and the use of sensitive relays, properly calibrated, the desired on and off control of a load, signal, recorder or the like may be obtained for any desired variation in photocell output. Further, the photocell may be replaced by any voltage or current source developing an output that varies with a preselected control factor.

It will also be apparent that the power current source 1 may be replaced by an alternating current power source and a rectifier or, if the load or power relay to is designed to operate on alternating current, it is preferable to insert a conventional rectifier in one of the leads 22, 23 or 26 of the conjugate bridge arm through which the resetting current impulse is impressed upon the relays 2d, 2%. Further, sensitive relays may be inserted in any two or more arms of the bridge network. These relays may be of any desired sensitivity, all alike or each difierent, to obtain various types of multiple control.

The power relay 8a may advantageously be of the time delay type in certain applications to prevent interruption of the load circuit during the interval within which the sensitive relays are reset. Such a time delay action is particularly desirable when the circuit is used as a photoelectric light control, thereby preventing false operation of the load circuit when clouds or smoke pass over the photocell.

The resetting current pulse is supplied by the load circuit power source in each of the above described relay circuits, but a separate current source may be employed for resetting the relay automatically at each contact closure. The manner in which a separate current source for resetting may be incorporated in the several relay to one bridge terminal, and the other battery terminal is connected through the relay switch 26, lead 23, the contacts of the resetting relay 2d, and lead 25 to the opposite bridge terminal. The method of operation of the Fig. '7 circuit will be apparent from the description of operation of the Fig. 6 circuit.

It will be apparent that the resetting current pulse must be a direct current when, as is usual, the sensitive instrument relay is of the direct current type. Direct current of appropriate polarity may be obtained from batteries, or from alternating current source through rectifiers. Alternating current may be employed in the load circuit or circuits of relay systems, such as shown in Fig. '7, in which a separate current source is provided for resetting, and also in relay circuits of the single power source type whe rectifiers are included in the load circuit to provide a direct current for resetting.

The stated modifications of the apparatus will be apparent to those skilled in the art and are pointed out to indicate the scope of the invention. It will be understood that further modifications and variations fall within the scope and spirit of the invention as defined in the following claims.

Iclaim:

l. A relay circuit comprising a current source having an output that varies with changes in a control factor, a sensitive instrument relay having a pointer carrying a contact of magnetic material for cooperation with a relatively fixed contact of magnetic material, a moving system including a coil connected to said current source for displacing said pointer in accordance with changes in the magnitude of the control factor, a load circuit controlled by the contacts of said instrument relay and including a power source of moving system to develop a high torque to overcome the magnetic attraction of and separate the engaged magnetic material contacts.

2'. A relay circuit as recited in claim 1, wherein said resetting circuit includes said power current source and a resistor for limiting the current flow established in said resetting circuit by said power current source.

3. A relay circuit as recited in claim 1, wherein said resetting circuit includes a source of current independent of said power current source.

A relay circuit comprising a current source having an output that varies with changes in the magnitude of a control tact-or, a sensitive relay having a pointer carrying a contact of magnetic material for cooperation with a relatively fixed contact of magnetic material, a moving system including a coil connected to said current source for displacing said point-er, a load circuit including a source of power current in series with said relay contacts and a load device, and a resetting circuit for establishing a current flow oi relatively high value through said moving syw to separate the relay contacts an engagement of the same; said resetting circuit ineluding saio. relay contacts in series with said power current source, said mo ding system, and a resistor for limiting the current'flow established through said moving system by said power our rentsource,

i i relay circuit as recited in claim in comloination with means electrically isolating said first current source from said power current source.

6. A. relay circuit as recited in claim l, in com hination with. means electrically isolating said first current source from said power current source, said means comprising a second coil on said moving system and included in said resetting circui.

7. A relay circuit as recited in claim in com hination with means electrically isolating said first current source from said power current source, said means comprising a balanced bridge network having said first current source and said resetting circuit as the conjugate arms thereof, said coil of the moving system of the relay being in one side arm of the bridge network.

8. A relay circuit comprising a current source having an output-that varies with the magnitude of a control factor, a sensitive instrument relay having a pointer carrying a contact of magnetic material for cooperation with a relatively fixed contact of magnetic material, a moving system including a coil connected to said current source for displacing said pointer, a load circuit including a source of power current in series with che relay contacts and a load device, a resistor in said load circuit, and a relay resetting circuit including said resistor and circuit elements connecting the same across said coil to establish a current flow through the coil when the load circuit is completed by a closure of the relay contacts.

9. A relay circuit comprising a current source having an output that varies with the magnitude of a control factor, a sensitive instrument relay having a pointer carrying a contact of magnetic material for cooperation with a relatively fixed contact of magnetic material, a moving system including a coil connected to said current source for displacing said pointer, and a load circuit and relay resetting circuit each including a source of power current in series with said relay contacts; said load circuit including a load device,

and said resetting circuit including said moving system of the relay.

10. A relay circuit as recited in claim 9, wherein said load circuit and said resetting circuit have a common source of power current.

11. A relay circuit as recited in claim 9, wherein said load circuit includes a series resistor, and said resetting circuit is connected across said resistor.

A relay circuit comprising a current source having an output that varies with changes in a control factor, a pair or relays each having a moving system carrying a contact of magnetic ma terial for cooperation with a relatively fixed contact magnetic material, circuit elements connecting said. current source to the moving systems of said relays to displace the same in oppo site sense with reference to the respective fixed contacts, a, load circuit controlled hy the contacts or" one relay and including a power c rrent source and a load, and a resetting circuit including the moving system and contacts of at least one of said relays in series with a source of resetting current.

13. A relay circuit as claimed in claim 12, wherein said source of. resetting current com= prises a voltage drop resistor in said load circuit.

14-. A relay circuit comprising e, current source havin an output that varies with changes in a control factor, a sensitive relay an op erating coil connected to said current source, said. relay having cooperating magnetic contacts controlling a load circuit, a resetting circuit for said sensitive relay; said resetting circiut in-= eluding resetting relay connected to said current source and having a coil controlling the en easement of a pair of contacts, and circuit elemerits connecting the contacts of the resetting relay in series with the coils of both relays and with a resetting current source, the polarity of said resetting current source being such that cur rent flow therefrom actuates both relays to separate the contacts thereof.

15. A relay circuit comprising a pair of magnetic contact type relays and impedances serially connected in a bridge network, a variable current source connected across one pair of opposite ter= minals oi the bridge network, the relays having moving systems that are displaced in opposite sense with reference to the fixed contacts there of upon a given change in the output of said source, a load circuit including the contacts of one relay in series with a load and a power current source, and a resetting circuit connected across the other pair of opposite terminals of the bridge network; said resetting circuit including the contacts or the resetting relay in series with a source of resetting current:

16. A relay circuit as claimed in claim 15, wherein said source of resetting current has an output of an order substantially higher than that of said variable current source.

17. A relay circuit as claimed in claim 15, wherein said source of resetting current comprises a. voltage drop resistor in said load circuit.

18. A relay circuit comprising a pair of magnetic contact type relays and impedances serially connected in a bridge network, a variable current source connected across one pair of opposite terminals of the bridge network, the relays having moving systems that are displaced in opposite sense with reference to the fixed contacts thereof upon a given change in the output of said source, a load circuit including the contacts of one relay in series with a load and a power current source,

and e resetting circuit connected across the other pair of opp site terminals of the bridge network; said resetting circuit including the contacts of both relays in series with a source of resetting current.

19. A relay circuit comprising e pair of sensitive relays connected to e control current source having an output that varies with n control teetor, impedances cooperating with said relays to form a bridge network across which said current source is connected as one conjugate arm, the first relay having magnetic contacts that engage when the output of ssid current source tells to n selected value and the second relsy having magnetic contacts that engage when said output rises to another preselected value, a power current source and e load in, series with the contacts of one relay to form a, controlled circuit, and a, resetting circuit connected as the other conjugate arm of the network and including the contacts of both relays in series with each other end with a source of resetting current, the polarity of said resetting current source being such that the rumtrol and resetting currents are adfiitlve in the first relay and opposed in the second relay.

ANTHONY H. LAW. 

